I haven't used one myself yet, but have read a lot about it.From what I can gather, quality control has been an issue; if you get a good one they're great, but there have been (are?) some poor samples about so make sure you buy from someone who'll exchange a duffer.Distortion and vignetting can be a problem unless you're using software than correct it eg LR/ACR.The other 'issues' like manual focus and iris don't seem to bother the people using them much.

i felt vignetting at 2.8 was quite extreme though - yet OK at smaller apertures

online info available on this lens did not seem to mention two aspects though:

1) significant focus shift when changing aperture - as this lens is 100% manual (including stopping down aperture) this took a bit to get used to and compensate for 2) the distance markings on the focus ring of my copy were wayyy off - i used adhesive tape and marked i.e. 1m / 2m / 3m / 5m / infinity at two diff. apertures to work with.

if you are not in a terrible hurry resp. use i.e focus work arounds i found it to be awesome value for money.

cheers

ps:

i also put together a comparison of samyang 14mm to EF L 14mm and the samyang 85mm vs. canon 85mm 1.8 based on photozone.de review data - see attached image

I have had the Samyang 14mm for a couple of days and I cannot get over how sharp this thing is. It is amazing. Very minimal CA as well. The field is very flat when focusing at infinity. The detail at the edges is very very good. Focusing at closer range introduces some field curvature.Great for landscapes! Certainaly better than the Canon 14mm II.

On the down side:Manual aperture ring and doesnt show aperture in the image Exif .Also high barrel distortion and vignetting.

To get maximum sharpness across the frame and into the corners I found it is important where you put the focus. I spent some time testing and made a mark on the distance scale.

I also found if you use the distance scale, and say focusing on 2metres you will get a different focus point depending on whether you bring the focus down from the infinity to 2 metres or up from minimum focus up to 2metres. I now always focus in the one direction if using the distance scale.

To get maximum sharpness across the frame and into the corners I found it is important where you put the focus. I spent some time testing and made a mark on the distance scale.

I also found if you use the distance scale, and say focusing on 2metres you will get a different focus point depending on whether you bring the focus down from the infinity to 2 metres or up from minimum focus up to 2metres. I now always focus in the one direction if using the distance scale.

Seems pretty good to me. The only drawback is that it's been made for shooting @ f2.8 so there's too much vignetting correction if you're shooting stopped down.

I have made one for f8, but there seems to be a difficulty in LR seeing different profiles for the same lens. I spent quite a lot of time trying to get LR to offer it and have a alternatives for different stops, but without much luck. I ought to have another try to resolve the issue, but I find the one above works sufficiently well anyway.

I just got it and have taken it out for wide field astrophotography. It performs very well wide open out to the edges on an APS-C camera. Exam of individual frames at 100% shows good sharp stars. This is a lens that focuses nicely in Live View. It does vignette like crazy. I was shocked when I shot my flat field stack (evenly illuminated oof diffused light filling frame) for the astro-stack program (Lynkeos, if anyone cares). I will post the stack results later. I haven't done much with it in daylight. The mustache distortion is wicked for man-made objects, I gather.

It has mustache distortion, but it's sharp and has surprisingly ultra-low levels of chromatic abberation compared to the competition. It is really quite remarkable how well controlled the CA is on this lens. Better than Nikon and Canon, and probably even Zeiss.